In recent years, in order to prevent the loss of data stored in a memory apparatus in the event of a failure or a disaster, measures are being taken to achieve the redundancy of data, for instance, by connecting a plurality of physically-separated sites with a communication line, sending data of a primary logical device in a primary memory apparatus installed at a primary site to a secondary memory apparatus installed at a remote secondary site via a communication line, and recording such data in the secondary logical device of the secondary memory apparatus at the secondary site.
Remote copy is known as backup technology for achieving the redundancy of data. Remote copy is a technique of setting copy-target volumes in a primary memory apparatus as the copy source and a secondary memory apparatus as the copy destination, and copying data from the primary logical device to the secondary logical device so that data of the primary logical device in the primary memory apparatus and data of the secondary logical device in the secondary memory apparatus will mutually coincide.
By using the remote copy technique, with corporations, for instance, it will be possible to consolidate, in real time, data of memory apparatuses of the respective sites in the memory apparatuses within the data center. Incidentally, the pair configured from a primary logical device and a secondary logical device is referred to as a remote copy pair. In order to create a remote copy pair, it is necessary to copy all data of the primary logical device to the secondary logical device. This copy process is referred to as an initial copy.
Normally, the initial copy is performed with a method of transferring remote copy target data in the primary memory apparatus via a network connecting the primary memory apparatus and the secondary memory apparatus. However, with this method, since vast amounts of data are transferred via the communication network connecting the primary memory apparatus and the secondary memory apparatus during the initial copy, it is necessary to prepare a broadband communication network even in a low-load I/O (Input/Output) processing environment, and this led to a wasteful business investment.
Moreover, for users under a contract of paying a traffic charge for the communication network (communication line) connecting the primary memory apparatus and the secondary memory apparatus, this will lead to a wasteful investment since users must pay a fee in accordance with the data traffic required for the initial copy.
In light of the above, a method has been proposed to reduce the data traffic between sites as much as possible during the initial copy. Specifically, with this method, a snapshot is created between a copy source logical device and an intermediate logical device in a memory apparatus at a first site (primary site), the pair status of the snapshot is thereafter separated, a logical device corresponding to the intermediate logical device is subsequently formed in an external memory apparatus (portable memory medium), the external memory apparatus is transported to a second site (secondary site) using a transportation means, the logical device formed in the external memory apparatus is registered in the memory apparatus at the second site, and only differential information that differs from the logical device formed in the external memory apparatus is thereafter copied from the memory apparatus at the first site to the memory apparatus at the second site via a global network (refer to Patent Document 1).